High speed electric typewriters and data input keyboards for computer systems require switch keys which operate reliably over a relatively long service life and which also provide a desirable tactile feel when they are pressed. In modern keyboards, the profile of the switches must be sufficiently low to provide a maximum height of about 30 millimeters for key switches in the third row of the keyboard. Moreover, in view of the large number of keys required for keyboards, keys must be relatively easy to assemble and should preferably be structured to allow rapid automatic assembly.
Low profile keys must also provide a relatively long key stroke of, for example, 4 millimeters. Each key should preferably operate with hysteresis to provide a slightly delayed actuation of switch contacts over the pressing key stroke and a corresponding delayed opening of the contacts when the key is released. This hysteresis behavior is required from a human engineering standpoint to avoid inadvertent operations and multiple operations of the switch when it is pressed and then released.
It is therefore an object of the invention to provide a relatively low profile switch which avoids inadvertent operations and multiple operations of switch contacts.
A further object of the invention is to provide such a low profile switch with contacts which are opened and closed with a hysteresis operation.
Another object of the invention is to provide a switch with a relatively low profile in relation to its key stroke.
A further object of the invention is to provide a low profile switch which is reliable in operation over a relatively long life and which may be easily and automatically assembled.
Another object of the invention is to provide a key switch which requires a perceptible increase in operative pressure to close its contacts.